The present invention relates to generally tube-like structures, e.g., conduits, needles, catheters, cannula, etc., their rigidity and flexibility, how to make and use them, and how to change and use their degree of rigidity or flexibility. More particularly, it relates to a cannula for insertion into body tissue, and to a method for inserting the cannula into the tissue. More particularly, the present invention relates to an infusion cannula of an infusion appliance.
In a great many therapeutic or diagnostic applications, uses or treatments, it is necessary for a cannula to be provided inside body tissue over quite a long period of time, for example in order to permit repeated or sustained administration of therapeutic or diagnostic fluids. In the treatment of patients with diabetes, for example, insulin from an infusion appliance is administered at regular intervals through a cannula which remains in the patient's body tissue over a period of several days.
For this purpose, it is known from U.S. Pat. No. 4,562,751, for example, to use a steel cannula. A steel cannula does have a simple structure, but it also has various disadvantages. The sharp needle tip of the rigid cannula can cause constant irritation of the surrounding tissue since it cannot adapt to movements of the tissue. Such a rigid cannula, when inserted, is uncomfortable for the patient or even painful. There is also a considerable risk of needlestick injuries when removing the needle-like cannula from the tissue.
Devices referred to as soft cannulas and which are flexible have therefore been developed. U.S. Pat. No. 4,755,173, for example, describes an injection set used for subcutaneous administration of a fluid, in which a steel needle is guided through a soft cannula so that the sharp tip of the steel needle protrudes from the soft cannula. With the aid of the steel needle, the soft cannula is inserted into body tissue. The steel needle is then removed from the soft cannula, as a result of which a fluid connection is established between the soft cannula and the tissue.
A soft cannula of this kind can easily follow the movements of the tissue, so that there is no irritation of the surrounding tissue. To insert the soft cannula, however, it is still necessary to use a rigid cannula, for example a steel cannula, which has to be removed after the soft cannula has been inserted. The soft cannula therefore also poses a risk of a needlestick injury. In addition, the opening through which the steel cannula has been removed has to be sealed off to permit correct use of the cannula. This procedure is complicated and increases the risk of a lack of leaktightness when fitting the cannula, for example in an infusion appliance.